This proposal discusses two lines of invesigation pertaining to study of the genetic regulation of galactose metabolism in the eucaryote Saccharomyces cerevisiae. The first section describes procedures for detecting and cloning yeast DNA fragments containing genes encoding the proteins responsible for metabolism of galactose and the proteins involved in the regulation of this process. These include the GAL 1, 10, 7 cluster, which encodes the three Leloir enzymes, and the GAL 4 gal c complex, which encodes the galactose activator protein. Several methods for identifying these specific DNA fragments are proposed. The second line of investigation concerns two genetic experiments designed to generate mutant strains which will resolve specific questions concerning the mechanism of galactose regulation and which will also facilitate further biochemical experiments anticipated in the future. The first experiment proposes a method for isolating a set of GAL 1 deletion strains, which will be used to produce a fine-structure map of the locus. The second experiment describes a selection procedure for isolating activator independent mutations linked to the GAL 1, 10, 7 cluster. I anticipate that the results of this work will facilitate the study of galactose regulation in yeast, which in turn will provide insight into the mechanism by which genetic expression is regulated in any eucaryotic cell.